Estimation of Series- and Shunt-Capacitances of a Single-Phase Core-Type Transformer Windings

Estimation of capacitance is essential in order to understand the capacitive coupling in the windings, and to assess the health of the transformer. The estimation of the series capacitance (C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ) of a transformer winding from the terminal data will be challenging due to the effect of interwinding capacitance (C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</inf> ) between the HV windings. It is essential to decouple the effect of C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">w</inf> to measure series capacitance accurately. In this paper, an equivalent ladder circuit model of a single-phase, core-type transformer is considered and each HV winding is represented as an electro-magnetically coupled lumped ladder circuit model. Initially, the high-frequency behaviour of the model is analysed. After that, a specific frequency is identified to capture the capacitive voltage distribution along the circuit model. Based on the voltage data, connections between specific locations are proposed such that the influence of the inter-winding capacitance is minimised. As a result, accurate estimation of C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> can be possible with minimum complexity. With the proposed methodology, it is possible to estimate the capacitances of any core-type transformer even if their design details are not available. The capability of the proposed method is demonstrated on electrically and magnetically coupled, physically realizable 4-section and 6-section ladder networks of 1-phase, core-type transformers.